1

To begin with, I'm clearly not a physicist but I'm certainly interested by several physics questioning.

So, my question here is, according to Einstein's relativity, I understood that travelling at the speed of light would be instantaneous due to space and time dilation. Then, from the point of view of a photon that goes from the sun in direction of the earth, what is the duration of its journey? I know that from our point of view it takes about 8 minutes.

Could you please indicate me if I missed something?

Qmechanic
  • 201,751
Vincent Robert
  • 11
  • 3
    In a sense, your question is unanswerable (some would even say it's meaningless within the framework of relativity) because a photon doesn't have a rest frame. But we have numerous questions on this topic here, eg https://physics.stackexchange.com/q/16018/123208 & https://physics.stackexchange.com/q/54162/123208 and the links therein. – PM 2Ring Nov 12 '20 at 22:07
  • 2
    Does this answer your question? How does a photon experience space and time? – PM 2Ring Nov 12 '20 at 23:24
  • Thanks for your references. Unfortunately, I don't think I have enough knowledge on the subject to understand how those questions are linked to mine. I'm sorry. I think I will need some more time to really get into relativity. – Vincent Robert Nov 13 '20 at 08:22
  • Ah, ok. I linked those questions because when you ask "what's happening for light itself?", you're essentially asking what's happening in light's rest frame. Like if you're in a car that's travelling on a smooth road at constant speed you can consider yourself at rest in the car, and things in the car behave just the same as when the car is parked. Eg, if you drop something it falls straight down, relative to you, but to someone standing on the side of the road the object you dropped doesn't go straight down relative to their rest frame, instead it travels forwards, with the car. – PM 2Ring Nov 13 '20 at 10:16
  • (cont) However, relativity tells us that light doesn't have a rest frame, and that's one of the core insights that led Einstein to develop relativity. Light is dynamic, an oscillating electromagnetic wave. Einstein realised that if light had a rest frame, then in that frame the oscillation would be "frozen", but that's not consistent with Maxwell's equations, which are very successful at modelling all electromagnetic phenomena. – PM 2Ring Nov 13 '20 at 10:38
  • I'm not trying to write an answer in the comments (and we can't answer questions while they're closed), but hopefully what I've written will help you to see how the linked questions (and the links in those questions) apply to your question. If they don't, you're welcome to [edit] this question and explain what bits you don't get, so we can perhaps point you to other existing answers, or write fresh ones for you. – PM 2Ring Nov 13 '20 at 10:38
  • Many thanks to your explanation! Now I get the idea of the rest frame thanks to you.... Actually it reminds me of an exercise I did in high school on this topic (just replace the car by a bike). I think I will try to dig in other questions to get a better understanding. Thanks a lot. – Vincent Robert Nov 14 '20 at 11:16

1 Answers1

0

You can think of it as the limit of the time of travel of any object when approaching light speed.

From the frame of the moving object the distance between earth and sun shrinks, and the time of the trip decreases. The limit is zero distance and zero time, even while the limit is never reached.

It is like the infinite sums in math, that have a defined value, but that value is never obtained for any given number of terms.

But remember that for any velocity, if the traveller measures the light speed coming from the sun, it is not different from what we measure here.

Claudio Saspinski
  • 16,319
  • Thanks for your answer. According to your description I would ask again : then what's hapoening for light itself? Does time and duration decrease to 0? – Vincent Robert Nov 13 '20 at 08:25